1. Field of the Invention
The present invention relates to magnetic recording media, and more particularly, relates to a magnetic recording medium which has improved electromagnetic conversion characteristics and error rates by improvement in surface properties of a magnetic layer.
2. Description of the Related Art
In magnetic recording media used for video recorders, audio apparatuses, computers, and the like, particularly in recent years, there has been an increasing trend toward higher recording density, and in order to meet the trend described above, development of smaller minimum recording unit has been pursued, for example, by shortening recording wavelengths, decreasing recording track widths, and decreasing the thicknesses of recording media. Concomitant with the development described above, movement of making magnetic layers smaller have been in progress, and hence, in recent years, ferromagnetic metal powders or hexagonal ferrite magnetic powders, having fine particle sizes and large magnetic energy, have begun to be used.
However, as thicknesses of the magnetic layers are reduced, surface properties thereof are significantly affected by the state of asperities on surfaces of non-magnetic layers provided under the magnetic layers. Consequently, surface properties of the non-magnetic layers must be taken into consideration in order to ensure excellent surface properties of the magnetic layers. In particular, when a fine non-magnetic powder is contained in the non-magnetic layer, the dispersibility of the non-magnetic powder tends to become inadequate. As a result, the surface property of the non-magnetic layer and, by extension, the surface property of the magnetic layer may be degraded and, thereby, the electromagnetic transducing characteristic may be degraded.
As techniques relating to improvement in surface properties of magnetic layers, for example, a magnetic recording medium has been disclosed in Japanese Unexamined Patent Application Publication No. 2002-312920 in which the ratio of protrusions of an abrasive having a height of 15 nm or more, which is measured by an atomic force microscope (hereinafter referred to as an “AFM”), with respect to a predetermined area of a magnetic layer surface is controlled in a predetermined range so that a magnetic recording medium having high output, high recording density, and superior running durability can be realized. In addition, in Japanese Unexamined Patent Application Publication No. 2001-331924, a magnetic recording medium has been disclosed which has high density recording properties, superior electromagnetic conversion characteristics having durability, and superior handling properties in a manufacturing process. In the magnetic recording medium described above, the ratio of the total area of protrusions on the magnetic layer having a height of 10 nm or more, measured by an AFM, from a reference surface is controlled in a predetermined range, and at least one of a fatty acid and a fatty acid ester is contained in at least one of the magnetic layer and the non-magnetic layer provided thereunder so that the surface lubricant index is controlled in a predetermined range.
Furthermore, a magnetic recording medium has been disclosed in Japanese Unexamined Patent Application Publication No. 2002-367140, in which the ratio of protrusions on a surface of a magnetic layer containing a hexagonal ferrite magnetic powder, the protrusions having predetermined diameter and height, is controlled in a predetermined range so as to suppress the generation of thermal asperity (TA) and realize superior high density properties at the same time.
As described above, in response to recent requirements of higher recording density of magnetic recording media, it is required to realize a magnetic recording medium in which an excellent surface property of the magnetic layer can be ensured in spite of the reduction in the magnetic layer thickness and the reduction in the particle size of magnetic powder or non-magnetic powder and, thereby, a higher recording density and medium characteristics such as electromagnetic transducing characteristics, e.g., an S/N ratio (SNR), an error rate, and the like, become simultaneously compatible.